Field stars

Oxygen abundances in clusters show solar [O/Fe] ratios overall, and fall within the envelope of the distribution with [Fe/H] displayed by the disk field stars... 

The a-elements Mg, Ca, and Ti generally show solar ratios as well, while the [Si/Fe] value is enhanced slightly in the average ( 0.1) in the clusters. Compared to the behavior for field stars, the clusters do not show the slightly enhanced [Mg/Fe] or [Ti/Fe] values seen in the fields stars at the same [Fe/H]. 

Ca/Fe] agrees very closely with the field stars, while [Si/Fe] is somewhat more enhanced in the clusters stars compared to the field stars at the same metallicity. 

Unlike the field stars, the open clusters show enhanced values of [Na/Fe] ( 0.2) and [Al/Fe] ( 0.1). Sodium and aluminum seem to be high and show a large dispersion at all ages and Galactocentric distances. There is recent evidence that... 

Abstract. In this contribution we present the results based on high-resolution spectra of 45 clump stars of the Galactic field. The main atmospheric parameters and abundances of 12C, 13C, N, O and other mixing sensitive chemical elements were investigated. Elemental ratios in the sample of field stars are compared to the results available for evolved stars in open clusters and to the theoretical prediction of extra mixing in stellar interiors. 

Abstract. The astrophysical origins of the element fluorine remain uncertain due in part to the availability of just a small number of abundance results for this element, that has readily observable transitions only in the infrared via vibration-rotation lines of HF. In this paper, we discuss all the available Galactic fluorine abundances to date, and add results for field stars with metallicities between [Fe/H] = -0.5 and -1.0, plus two stars that are members of the Orion association. The fluorine abundances obtained for the young Orion members are found to be in agreement with the trend of [F/O] versus O observed for the disk and they are a good representation of the present day value in the Galactic disk. 

Abundance Variations in the Galactic Disk Planetary Nebulae, Open Clusters and Field Stars... 

The metallicity distribution of globular clusters in the Galaxy has a metal-rich peak at [Fe/H] -0.5 and a metal-poor peak at [Fe/H] -1.6 (e.g. Cote 1999), where most of the metal-rich ones are bulge clusters. Metallicities for samples of field stars were derived by McWilliam Rich (1994, hereafter MR94), Sadler et al. (1996), Ramirez et al. (2000). Zoccali et al. (2003) presented the... 

Fig. 2. Left, middle and right panel run of the [C/Fe], [N/Fe] and carbon isotopic ratios with absolute magnitude. Filled triangles, circles and squares are dwarfs/subgiants in NGC 6397, NGC 6752 and 47 Tuc, respectively ([7]). Open symbols are RGB stars in the same clusters, from a number of literature studies (see [7] for references). Crosses are the field stars from [4].

Thus, no unevolved star seems to be polluted by cluster giants with composition typical of field stars. On the other hand, we are not aware of any physical mechanism able to select only N-rich giants in order to form binary systems and pollute their companions, as in the scenario devised by [12]. 

In addition to results from this study, Table 1 includes two of the relatively more metal-rich globular clusters associated with the Sgr dSph. There appears to be little in common between the two metallicity groups in their < a>-abundances relative to iron. Abundances reported so far for in situ Sgr dSph field stars of comparable metallicities [4] are in accord with those of its metal-rich clusters. 

C. Sneden, I. I. Ivans, J. P. Fulbright Globular Clusters and Halo Field Stars . In Origin and Evolution of the Elements Volume 4, Carnegie Observatories Astrophysics Series, ed. by A. McWilliam, M. Rauch (Cambridge, 2004)... 

The correlations and anti-correlations among these elements for stars in GCs and the range of variation of each element resemble those of proton-burning. They appear to be independent of stellar evolutionary state, with the exception that enhanced depletion of C and of O is sometimes seen just at the RGB tip. This extra depletion of O just near the RGB tip is seen in our M13 data shown (see also Sneden et al 2004). Metal poor halo field stars, however, show no evidence for O burning (Gratton et al 2000) or Na enhancement. The variations seen in the field stars are much closer to those predicted by classical stellar evolution that those seen in the GC stars. 

Fig. 1. The range of [C/Fe] (left panel) and [N/Fe] (right panel) is shown as a function of metallicity ([Fe/H]) for the globular clusters from our work on M71, M5, M13, and M15 as well as for 47 Tuc (from Briley et al 2004a). Large samples of stars, mostly subgiants, were used in each case. Each GC is represented by a horizontal line. The characteristic field star ratio, from Carretta, Gratton Sneden (2000) for C and from Henry, Edmunds Koppen (2000) for N, are indicated by vertical arrows in each panel.

Spectroscopic observations of globular clusters (GCs) have revealed star-to-star inhomogeneities in the light metals that are not observed in field stars. These light metal anomalies could be interpreted with a self-pollution scenario. But what about heavier (Z > 30) elements Do they also show abundance anomalies Up to now, no model has been developed for the synthesis of n-capture elements in GCs, and the self-pollution models do not explain the origin of their metallicity. In 1988, Truran suggested a test for the self-enrichment scenario [4], which could possibly explain the metallicity and the heavy metal abundances in GCs if self-enrichment occurred in GCs, even the most metal-rich clusters would show both high [a/Fe] ratios and r-process dominated heavy elements patterns, which characterize massive star ejecta as it is seen in the most metal-poor stars. 

Table 1 lists our abundances of Fe, C, O and a-elements for the observed clusters. An overall excess of a-elements is shared by all the clusters up to solar metallicity, consistent with SNell being responsible for the gas enrichment. Our findings are also in good agreement both with all previous high resolution studies (see [2], [3], [6]) and with recent abundance determinations for field stars in the Galactic Bulge (see [10]). 

Globular clusters are quite distant and their turnoff (TO) stars are intrinsically relatively faint. Following the advent of state-of-the-art instrumentation in 4m class telescopes, the first Li observations were carried on in GC stars, while with the advent of 8m class telescopes a quality jump occurred high quality spectra can now be obtained for the TO stars of the closest clusters, comparable to that available for field stars. In spite of this advancement, only a handful of published refereed papers have been devoted to the study of Li in globular cluster stars, and only one to beryllium. Based upon the wealth of information made available as a result of this data, I will present new findings concerning stellar mixing, primordial Li production and GC formation. 

Fig. 3. Beryllium spectra for the two NGC6397 stars observed by Pasquini et al. 2004. The spectrum of a comparison field star is also added. Best fit models (red dots) are overimposed.

That is, the straightforward interpretation of abundance data for Galactic field stars in terms of stellar populations is feasible only because the Galaxy apparently acquired its gas early, or at a rate which was well-matched to the star formation rate across the whole volume now sampled by local halo stars, and kept this gas well-mixed and because the stellar IMF is (close to) invariant over time and metallicity. Neither deduction was obvious, nor is the underlying physics understood. However, these two deductions apply so well they have become assumed authors use any violation to rule out some possible Galaxy merger histories, as in the Venn et al. analysis from which Figure 1 is taken. 

Fig. 1. Element ratio data for Galactic field stars (dots) compiled by Venn et al. (2004). [The open squares are stars in dSph galaxies.] The important point to notice here is the very small scatter in element abundances for Galactic field stars at any given [Fe/H] value, over 4dex in [Fe/H].

Fig. 2. Top panel Observed (UVES POP [1]) and synthetic Ha profiles of the field star HD 140283. The unmerged data (2001-07-09, frame 570) was retrieved from [1] and rectified using a parabola interpolated from the continua of adjacent orders. A best-fit Teff of 5760 K (at log <7 = 3.67 and [Fe/H] = —2.4, neither critical) is indicated.

It is particularly interesting to see that we derive a higher effective temperature for the reference field star HD 140283 (5650 K, while [3] give 5560 K), but a markedly lower effective temperature for the cluster turnoff star (6230 K vs. 6480 K). Seemingly, the subgiant is sufficiently cool (5480 K) such that the (weak) intrinsic profile of Ha could even be recovered from the UVES pipeline spectrum. Observational problems dominate and drastically limit the temperature determination and its reliability. 

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